1. Field of the Invention
This invention relates to a dry etching process and, in particular, to a dry etching process utilizing a magnetron discharge.
2. Description of the Prior Art
Recently, a reactive ion etching technique has primarily been used in a fine patterning for the fabrication of a high density device. The reactive ion etching technique comprises introducing a gas containing halogen atoms, such as CF.sub.4, into a chamber holding a substrate placed on one of a pair of oppositely facing electrodes, applying high frequency power across the pair of electrodes to discharge that gas, and etching the substrate through the utilization of ions and radicals produced due to the discharge.
As an etching apparatus for performing such an etching process, two types of apparatus are known:
(1) a batch-wafer apparatus for etching, for example, 10 to 20 substrates at a time within a large-sized chamber and (2) a single-wafer apparatus for etching only one substrate within a small-sized chamber. LSI patterns will become more and more micro-miniaturized in the future and, furthermore, the silicon wafer diameters will also been more and more enlarged in the future, as in an 8-, 12-inch . . . size. In order for a very fine pattern to be uniformly formed on the surface of the greater-sized wafer, the single-wafer apparatus has been found advantageous over the batch-wafer apparatus and thus has largely been employed as such. Under the identical etching-rate conditions, however, the single-wafer apparatus is lower in processing capability than the batch-wafer apparatus. In the single-wafer apparatus, an ingenious design has been made to enhance the discharge efficiency, such as to utilize magnetron discharge under a magnetic field.
The conventional dry etching apparatus utilizing the magnetron discharge is shown in FIG. 1. In the arrangement shown in FIG. 1, reference numeral 11 shows a vacuum chamber; 12, a cathode; 13, a sample; 14, a matching circuit; 15, a high frequency power source; 16, a magnetic field generator having a plurality of magnet bars 16a arranged in an order of N, S, N and S; 17, a driving mechanism for moving magnetic field generator 16 in a direction parallel to cathode 12; 18 and 19, a gas inlet and gas outlet, respectively; and 20, an insulator. In this apparatus, electrons are cycloidally moved at a perpendicular intersection area of a magnetic field generated at magnetic field generator 16 and an electric field crossing an ion sheath created in the neighborhood of the surface of cathode 12. As a result, a dense plasma is created at that location and the sample is etched at a high rate due to the ions in the resultant plasma. The reciprocating movement of magnetic field generator 16 assures a uniform formation of the plasma and thus a uniform etching of sample 13.
The apparatus as shown in FIG. 1, however, has encountered the following problems.
As shown in FIG. 2A, dense plasma region 21 over a clearance between magnet bars 16a creates a space potential difference relative to the other region, resulting in bending the ions in their moving direction which are to be incident vertically on the sample. However, the bending of the ions never occurs in a direction orthogonal to the moving (scanning) direction of the magnetic field. As shown in FIG. 2B, the unmasked portion of sample 23 other than mask 22 is vertically etched in the direction parallel to the scanning direction of the magnetic field. As shown in FIG. 2C, however, "undercutting" occurs in a direction perpendicular to the scanning direction of the magnetic field. That is, the pattern configuration or profile differs depending on directions.
Even in the ordinary reactive ion etching never utilizing the magnetron discharge, if an aluminum film, for example, is etched by chlorine series reactive ions, a side etching occurs due to a violent reactivity of the activated chlorine. It is, therefore, difficult to make an etching at a desired side wall angle. Recently, a strong demand has been made for the technique of forming a groove of a greater aspect ratio (etching depth/pattern width ratio), i.e., the ratio of the etching depth to the pattern width, in the manufacturing process of the semiconductor device.